Name

glBindAttribLocation — associate a generic vertex attribute index with a named attribute variable

C Specification

void glBindAttribLocation(

GLuint program,

GLuint index,

const GLchar *name);

Parameters

program

Specifies the handle of the program object in
which the association is to be made.

index

Specifies the index of the generic vertex
attribute to be bound.

name

Specifies a null terminated string containing
the name of the vertex shader attribute variable to
which index is to be
bound.

Description

glBindAttribLocation is used to
associate a user-defined attribute variable in the program
object specified by program with a
generic vertex attribute index. The name of the user-defined
attribute variable is passed as a null terminated string in
name. The generic vertex attribute index
to be bound to this variable is specified by
index. When
program is made part of current state,
values provided via the generic vertex attribute
index will modify the value of the
user-defined attribute variable specified by
name.

If name refers to a matrix
attribute variable, index refers to the
first column of the matrix. Other matrix columns are then
automatically bound to locations index+1
for a matrix of type mat2; index+1 and
index+2 for a matrix of type mat3; and
index+1, index+2,
and index+3 for a matrix of type
mat4.

This command makes it possible for vertex shaders to use
descriptive names for attribute variables rather than generic
variables that are numbered from 0 to
GL_MAX_VERTEX_ATTRIBS -1. The values sent
to each generic attribute index are part of current state, just
like standard vertex attributes such as color, normal, and
vertex position. If a different program object is made current
by calling
glUseProgram,
the generic vertex attributes are tracked in such a way that the
same values will be observed by attributes in the new program
object that are also bound to
index.

Attribute variable
name-to-generic attribute index bindings for a program object
can be explicitly assigned at any time by calling
glBindAttribLocation. Attribute bindings do
not go into effect until
glLinkProgram
is called. After a program object has been linked successfully,
the index values for generic attributes remain fixed (and their
values can be queried) until the next link command
occurs.

Applications are not allowed to bind any of the standard
OpenGL vertex attributes using this command, as they are bound
automatically when needed. Any attribute binding that occurs
after the program object has been linked will not take effect
until the next time the program object is linked.

Notes

glBindAttribLocation can be called
before any vertex shader objects are bound to the specified
program object. It is also permissible to bind a generic
attribute index to an attribute variable name that is never used
in a vertex shader.

If name was bound previously, that
information is lost. Thus you cannot bind one user-defined
attribute variable to multiple indices, but you can bind
multiple user-defined attribute variables to the same
index.

Applications are allowed to bind more than one
user-defined attribute variable to the same generic vertex
attribute index. This is called aliasing,
and it is allowed only if just one of the aliased attributes is
active in the executable program, or if no path through the
shader consumes more than one attribute of a set of attributes
aliased to the same location. The compiler and linker are
allowed to assume that no aliasing is done and are free to
employ optimizations that work only in the absence of aliasing.
OpenGL implementations are not required to do error checking to
detect aliasing. Because there is no way to bind standard
attributes, it is not possible to alias generic attributes with
conventional ones (except for generic attribute 0).

Active attributes that are not explicitly bound will be
bound by the linker when
glLinkProgram
is called. The locations assigned can be queried by calling
glGetAttribLocation.

OpenGL copies the name string when
glBindAttribLocation is called, so an
application may free its copy of the name
string immediately after the function returns.

Errors

GL_INVALID_VALUE is generated if
index is greater than or equal to
GL_MAX_VERTEX_ATTRIBS.

GL_INVALID_OPERATION is generated if
name starts with the reserved prefix
"gl_".

GL_INVALID_VALUE is generated if
program is not a value generated by
OpenGL.